1. Field of the Invention
The present invention relates to optical absorbers for long-wave infrared (LWIR) radiation applications, such as photodetectors, microbolometers and the like, and particularly to the enhancement of LWIR absorption in a dielectric substrate in order to increase device responsiveness through the generation of surface plasmons on the dielectric surface.
2. Description of the Related Art
Long-wave infrared (LWIR) radiation detection has recently become quite important in a wide variety of civilian, military and law enforcement applications, such as, for example, target detection, medical monitoring, automotive driver assistance and the like. LWIR radiation has a wavelength range between approximately 8 micrometers (μm) and 12 micrometers (μm). LWIR is particularly important in applications requiring optical absorption, such as in photodetectors, microbolometers and the like, and enhancement of optical absorption in a dielectric layer is of critical importance to the improvement of detection quality, device responsiveness and sensitivity.
The surface plasmon phenomenon has recently found applications in optics and photonics, such as in, for example, plasmonic waveguides, enhanced transmission through apertures, enhanced photo-luminescence and Raman scattering spectroscopy. It would be desirable to be able to enhance optical absorption using surface plasmons. Surface plasmons occur when optical wavelength electromagnetic waves interact with a sub-wavelength metal object, resulting in conduction electron oscillations. The oscillating electrons give rise to nano-plasmonic electric fields that become confined within sub-wavelength resolution areas near the metal with very high magnitudes.
Recently, there has been progress in generating surface plasmon enhanced absorption in the long-wave infrared range. For example, surface plasmon waves have been used to enhance sensitivity of quantum-well infrared detectors by using a periodic array of holes in a gold thin film. Additionally, surface plasmon waves have been used to enhance sensitivity of quantum-dot infrared detectors for focal plane arrays by using corrugated gold metal and metal photonic crystals. Further, a long-wave infrared focal plane array with enhanced noise-equivalent temperature difference was demonstrated by using a backside configured sub-wavelength hole-array plasmonic structure. Moreover, concentric double C-shaped plasmonic structures were used to enhance optical absorption in uncooled microbolometer pixels. However, such techniques are not only typically experimental, but typically are relatively difficult and expensive to implement for device manufacture. Thus, it would be desirable to utilize surface plasmon enhancement of optical absorption in an absorber which could be readily and easily manufactured.
Thus, an optical absorber for long-wave infrared radiation addressing the aforementioned problems is desired.